Most commodity and specialty organic chemicals used in the manufacture of polymers and other materials are derived from crude oil. For example, 1,6-hexanediol, one such chemical, is used as a starting material for polyesters, polyurethanes, and diacrylates, among others.
1,6-hexanediol has been made by processes in which cyclohexane, a hydrocarbon produced from steam cracking of oil, is initially converted to the carboxylic acid adipic acid or epsilon-hydroxycaprioc acid, the carboxylic acid is then esterified with an alcohol, and the resulting ester is reacted with hydrogen in the presence of a hydrogenation catalyst. This process is recognized as being disadvantageous because of the esterification step and because the hydrogenation reaction is conducted under high temperature and pressure. See, for example, JP-B-53-33567 which employs a copper hydrogenation catalyst in such a process.
Several processes have been disclosed for the production of 1,6-hexanediol from those same carboxylic acids, which processes do not include an esterification step. Those processes disclose the use of a variety of catalysts including cobalt, rhenium and Raney nickel. However, those processes employ relatively severe reaction conditions and/or suffer from unsatisfactory catalyst performance. Other processes have been disclosed which convert a salt of a carboxylic acid directly to the diol but, similarly to the acid conversion processes, the reaction conditions are extreme because of the use of cobalt catalysts.
Mitsubishi has reported the direct hydrogenation of a mixture of adipic acid and hydroxycaproic acid to 1,6-hexanediol using catalysts containing ruthenium, tin and platinum. See, for example, U.S. Pat. No. 5,969,194. However, the temperatures and pressures employed in the exemplified processes are economically undesirable and, thus, do not suggest a commercially viable process.
There remains a need for processes for the production of 1,6-hexanediol which do not suffer from the deficiencies of the prior art.